Was discussing this with my buddy and we think that the trunk mounted battery setup of the R53 should be relatively easy to make work in a R50. Anyone ever does this?

Isn't the floor of the R50 in the boot kinda flat? Unless I've seen wrong. The R53 has a box for the battery. You'd need all the cables, add the box if it's not there, etc.

There's a small well for the toolkit that also provides access to the bolt for the spare tire. If you want to fit a standard battery, you'll be cutting the trunk floor.