errr, drown, do we ?
I like a little bit of noodling around with plasticard offcuts. A square of leftover from a boat kit, some microstrip in the drawer for bits to short to go back in the packet and posts from some strip I cut for something else once.
A few minutes fiddling around gave me these stands. I didn't measure anything other than the backboards - and then only by placing the lifebelt on them to make sure it fitted. Somebody probably makes a kit for these but this was nice, easy and cheap.