I did not fill in all the gaps with foam or metal tape. I was afraid it would fill up with water like a bath tub in the rain. Actually thought about adding some drain holes in the floor but changed my mind at the last min.
My new 2020 chassis is mastic-sealed to the aluminium floor panels and it fills with water when we get caught in the rain. I have had to drill holes on the corners to let it drain. In a very wet Wales last year we had nearly an inch of slopping about water in the footwells, which didn't impress Mrs R1NGA very much (the mental scars will take a while to heal there I fear....)
