I have made some mistakes with my kit (because I'm a total beginner) so I would need some kind of putty. I will need to fill both small & relatively large gaps. I'm also planning on trading my Mr Surfacer 1000 for a different primer. I have a few questions to ask.
Would lacquer based primers fog up clear plastic? What would you need to thin Tamiya putty (basic type) & can you use Contacta Professional (the only glue that I have ATM) to thin the putty?
My local hardware stores don't sell Miliput (I live in Australia BTW) so will the following epoxy putty do? http://www.selleys.com.au/fillers-putty/epoxy/knead-it-aqua/
On styrene, I use a couple of methods for filling gaps, depending on the size of the gap.
If it's small, I prefer to use stretched sprue, using the kit sprue, where possible, and liquid cement for styrene. That way, I'm using like material with like, and the result is as homogeneous as possible. For larger gaps, I'll use sprue, or scraps of styrene sheet, on the same principle of like with like.
For putty with a styrene kit, I use Squadron white, thinned with acetone. I apply it in one of two ways. One is to put the putty in the gap and then using a cotton swab soaked in acetone to wipe away the excess, leaving putty just in the gap. The other is to put a dab of putty in a well on my ceramic palette, and then to add acetone with an eyedropper, and mix it till it's consistent. I call this my home-made Mr Surfacer. I apply this to the seam or gap with an old paint brush. Either way, the process leaves the putty in the seam or gap, but not on the surrounding area, reducing the amount of sanding afterwards.
If the gap is big enough, I'll fill it with scraps of plastic to fill the void as much as possible, and then use putty to fill the rest of it.
I have 2-part epoxies (eg, Aves A&B), and Miliput, but I don't like using those as filler. I find I wind up mixing too much more of the material than I really need, even when we're talking about an amount the size of a pea. I really use the 2-part epoxies more for sculpting.
I've used an automotive putty, too, but it was a 2-part putty, and again, it was really just more than I needed. But I don't discourage you from trying Bondo, or 3M's single-part putties.
Hope that helps!