I have the roof drawing for my 2015 Vegas 24.1. The Thor title for the series of 5 roof drawings is "Roof, Radius, Unit."
The spacing of the trusses on my RV indicates that Thor is not quite as symmetrical on their spacing as I would have expected (using house rafters as the comparison). For example, here is some of the spacing on my Vegas 24.1:
The trusses (11 of them) are 1 X 1 1/2 X .04 aluminum tubes. On mine they are spaced 16" apart; however, there is a huge void of trusses on mine from the 70 5/8 to 117 1/8 inch point from the rear with no trusses. The suggestion to use a stud finder is a good one since the trusses are all aluminum tubes and should show up well with a stud finder.
So my suggestion is before you start to drill into the roof, ask Thor for the drawings so that at least you have a general idea where to start looking for the trusses.
Ed & Bev Felker
Retired USAF Col and retired Nurse
Traveling with Lily & Bella ('Teddy Bear' breed)
2015 Vegas 24.1 (E-350)