I recently had to find a car seat solution for our old campervan (could only fit 1 3 point belt and had 2 Kids seats to fit. I came across the multimac which is a good solution for fitting more seats in comfortably, my order should arrive by the end of the month. Not cheap but it's crash tested and uses existing seatbelt mounts. The superclub should fit a model 3
Our full range of childseats and accessories
www.multimac.com