Filling air bubbles in an anero's product.

Hello.
It looks like I'm new to this board but I've been lurking on here for over a year. I've got most of the models. The question I have has to do with filling voids in an anero's maximus. See I bought a Maxiums and it didn't seem to move very well so I decided to modify it. I took it to a belt sander and made major modifications to the shape of it. I like it really well. So well that my partner wants to use it too!!! So I decided to get another one and modify it. Well after getting it to the shape that I want it has voids in the material from air bobbles. Do any of you know of any material that I can use to fill the air bobbles with. I don't want them to get filled up with ___ well you know what I mean. Thanks.

Viggen