Choosing fittings for a welded fuselage

[TonyG]

Happy weekend, everyone.

I'm at a point of having to make some decisions on my project and could sure use some input.

My project is a Stits SA6B Flutterbug, which has a welded 4130 tube fuselage. It's structurally complete, and now I'm pondering all the fittings that I may need down the road. I'm debating what can be attached to the structure with Adel clamps (or similar homemade fittings) and what needs to be bolted to a welded flange/other fitting. Is there a general rule of thumb for what SHOULD be hard mounted vs clamped? I'm specifically wondering about floorboards (all weight loads will still be transferred by resting on the structure), seatbacks/bottoms, the instrument panel, and a sheet metal panel that covers the top half of the fuselage from the cockpit forward.

In addition, there is a modification from the plans that the previous builder incorporated. The plans have a supplement for a brace in the rear cockpit. The builder modified the design, I guess to make it symmetric and more aesthetically pleasing. Unfortunately, it cuts down on available room and I have to lower myself into the rear cockpit using my arms because my knees won't clear otherwise. I'd rather not subject my passengers (i.e. wife...) to that. Is it worth it to remove the modification and weld it as designed, or am I likely to do more damage to the thin-walled tubing that it's currently welded to? I guess I could leave a healthy boss in place and not try to file down anywhere close to the longeron walls. Pictures of this part are attached.

Finally, I'm not sure if the previous builder oiled the inside of any of the tubing. What are the repercussions of burning off this oil while welding fittings? Will a simple re-oiling be sufficient?



-Tony