To elaborate on the Scamp standard "double" bed (I have a Boler
13 which I believe is the same measurements).
The side of the bed facing into the trailer is straight, but the side on the back wall of the trailer is somewhat of a "C" shape. In the middle, the bed is 48" (assuming a 4" thick mattress and that you run the bed right over to the closet/kitchen edges). At the side walls - well, about 6" in from the side walls since the really rounded part of the corner is hard to measure - it's about 41". Halfway between the side wall and the middle (so 1/4 of the way from head to foot), it's 46" wide.
Length (except in the extreme corners at the back), also with a 4" mattress, is just a scoch over 78".
Hope this helps,
PS: This is with Ensolite walls, which the older Scamps had too. I suppose newer Scamps with the Reflectix/rat fur might be a tiny bit smaller (guessing the walls coverings add up to a hair more).
PPS: Yes, I did just happen to be sitting in my Boler
with a tape measure to hand