Yes it is nice to be able to put your projects INSIDE something isn't it? You know, to hold everything together so it doesn't flop around? Discuss the techniques here!
this is long but very helpful hints in this, from my 4 years of autobody experience(repairing/welding and painting wrecked cars) i can assure you it is accurate
well first of all Bondo is the worst type of puddy you can get, its cheap, tends to pop out, and doesn't sand well. I suggest getting either Rage Gold of Liteweight puddy. rage Gold is sold at auto zone and not too much more than bondo.
second, puddy is not meant to hold to plastic, plastic and puddy expand/shrink and flex differently which would cause the puddy to pop out. Puddy is meant to put solely on metal or fiberglass. body filler/puddy IS NOT made to put on top of primer, it will not hold. you sand down body iller with 80-100 grit paper. some may say its too rough but they dont know what they are talking about, trust me. using higher grit takes a lot of time and a lot more work. puddy has been known to hold to some plastics, although not made to hold to plastic you should be okay to use it on a portable since it wont see weathering such as a car does. just be sure than wherever you know you will need to but puddy at, sand the plastic first with 80 grit paper so that puddy can "grip" better.
as for glazing puddy, its not meant to put on as normal filler/puddy. its not nearly as strong as normal filler and cant be applied nearly as thick. glazing puddy is meant to put on top of primer to fill in any small scratches/chips/dents you may have forgot. its convenient not to have to sand down all the primer to fix a small area. glazing puddy shouldnt be applied much more than 1-2mm thick, again its mainly just to fix deeper scratches that primer wouldnt cover
as for primers, auto zone or walmart sells some Duplicolor high build primer(and it sprays in a rectangle pattern not circle which is very nice to get more coverage) that works fairly well. its good for smaller projects like these when the good body shop grade primers arent applicable. ive used this primer and it holds fairly well. you spray the primer on with 2-3 coats let it "flash" in between. a flash time means the time it take the primer to partially dry so you can put another coat on without it running, but its not dry enough to handle. the flash time is about 5-10 min. if its a little humid or colder then wait a bit longer. You sand primer with 220 grit paper. primer will be dry enough to sand on 45 min after last coat. 3M paper is by far worth the extra price, it doesnt break apart in water and doesnt clog as fast as the cheap stuff. SAND WITH WATER(wet sanding or blocking), makes your paper last 10x longer and will not hurt the primer. you want to sand EVENLY until you start to see spots about the size of a dime show through. dont use your finger tips to press down when sanding, it will show in the paint. SAND IN LINES. NEVER sand in circles, it could show in your paint. You can spend $5 on a soft, spongy style sanding block(id recommend it if your case is curvy) or if you have mostly flat services i just use a wooden paint mixing stick, old school style. after you have sanded your project with 220, then put another 2-3 coats on it and then sand evenly with 400 grit paper. again sand down till little dime size spots show. 400 grit paper is the lowest grit paper you can use that wont show up in the paint, so dont skip this. Primer is meant to build up and LEVEL surfaces, thats why you put it on then sand it off to prevent a wavy look. it also does help paint to hold correctly.
almost finished. when ready to paint put the it on WET even coats, dont put on too much paint or it will run. as soon as it looks wet then stop spraying. a good paint system with very nice finishes are the model car spray paint cans, they are small spray cans and sorta expensive but you want your project to looks its best dont ya? its best to go with a base-coat clear-coat system to bring out the shine. Testors does pretty well the Laquer and Model Masters series both are pretty good. id suggest 2 cans of the color you want and just 1 can of clear coat, roughly about $15. the only down side, these paint take a lot of time to cure/set in properly before they can be handled. with actual car paints you have a hardener so curing is much faster, all non expensive paints are air drying. Depending on the transparency of you paint or if it has metallic, you may need more or less coats. usually about 4-6 LIGHT coats brings out a nice uniform color. again let it flash in between 5-10 min. it usualy takes 2 hours between color painting and clear coating. but you have a window of time to clear coat after you color paint it, about 24 hours before the color becomes too dry and you will have to sand on it to get the clear to stick, so just make sure you have time to do both. anyway, after the last application of clear coat it takes AT LEAST 24 hours to cure without worrying about finger prints, id suggest waiting 48 hours to be safe so your case looks its best.
lengthy, yes but it should help you out. any questions ill be glad to explain it better
to summerize what he just said in very basic terms bondo is NOT for anything structural, it is meant as a skim coat to cover up and flaws or imperfections in your case prior to paint
for portables bondo brand spot putty works well, my preference is to build my frankencases from whatever source materials at hand, using hot glue to hold the peices together then fusing them permanantly with liquid ABS plastic then sanding bondo and paint, you dont get stress cracks from seams because with the use of liquid ABS there arent any anymore
