I made the crosstie box that fits directly behind the seat in the aft fuselage. I messed up one of the channel pieces (cut side tabs in instead of out), so I had to re-do that piece. Otherwise pretty simple construction. I was paranoid about getting the thing assembled squarely, but it paid off and the assembly is as close to perfectly square as I can measure.
The plans say to rivet the top and leave the bottom clecoed; I chose to leave the whole thing unriveted until I see how it all fits in the fuselage...it will onlt take a few minutes to pop some rivets in at that time.