I'm currently in the throws of a 1978 Land Yacht International Tradewind renovation myself. Will be exciting to follow along with another one. I have no software or template, but will be interested to see if someone else does
(should have asked this myself) I have my own shell and frame graphs on a 1sq"-3sq" scale and a slightly larger 1sq"-5sq" project board. I cut out standard RV size beds/ sinks, shower, appliances, etc. from scrap paper and shift it around to play with different floor plan ideas on the board. It took about an hour to make my project board, and I figured it'd probably take more of my time and energy to learn a new program than to pull out the good ole fashioned scissors and construction paper haha.