New builder questions

Hello, my wife and I have been tossing around the idea of building a teardrop of our own and i think it's about time we get going on it. As such I have what is sure to be the first of many questions regarding it's construction. We were thinking of using 1X1 steel tubing to frame out the sides and for the ceiling ribs that will all be welded together and to the bottom frame. my first question is; will this be overkill? I would like to be able to climb my 300# butt up on top as we spend all summer at the drag races and it would be a good way to get a better view of the track. We also live in Alaska and where we camp there is a pretty good chance that we could end up with a 500+lb bear climbing on top (don't worry pics would follow!). My second question is; what would be the best method of attaching the side and ceiling panels to the metal frame? Our plans include using R-Tech expanded polystyrene with visqueen skin for the insulation (this is Alaska..) inbetween two panels with Starbrite on the roof and wood on the outside of the sides. We are probably going to use birch on the interior. Any advise is greatly appreciated!
Thanks, Jason Nilsson

Thanks, Jason Nilsson