Hey folks. I thought this might be worth a post. I followed the typical back/tank assembly advice, creating the slots in the backplate and then adding tabs to the inside of the tank.
To glue it on, instead of fiberglass or bondo, I used something else. This stuff:
I got familiar with it when I made my RC kit. Its a two part methacrylate, which is sort of like epoxy but a different chemistry that makes it less brittle. It bonds directly to the plastic, so it is not just filling the gap it is actually bonding them together. It sands very well, and has held up great on my RC kit for 3 years now. No pinholes, cracking or spalling. So I thought I'd give it a shot for this. After I got the tank trimmed as close to the contour of the backplate as I could, I started assembly and worked the mixture in place.
Lots of sanding later, and it looks pretty good!
I've got a few curing bubbles to fill in. Going to try some spot putty for that. I"ve never used it before but I'd like to try it, and since it doesn't have to be structural I think the spalling will be a non-issue.
A couple of good things about this devcon stuff - its strong, and its light. The tubes are 2.75 oz each, and i used just under 4 for all the gaps, and welding down the tabs. So that is around 11oz, minus whatever got sanded back off, which was a fair amount as you can see. SO probably around a half pound of weight is all I added this way.
The bad stuff - its NOXIOUS. You have to use it outside your house, at least in the garage. And you must wear a respirator. Otherwise you'll be seeing stuff, and not in a good way.
Its also kind of expensive. $6 a tube if you find it locally, but you can buy 10 packs on ebay for about $35. I used 4 tubes on the back, probably another tube and a half on the biceps, and I haven't done the shins yet. So a 10 pack may be just enough for this kit.
Anyway, hope this was a helpful alternative. Good luck! This seems to be the hardest part of this kit. So I'm hoping to get it out of the way as fast as possible.
-Brian