I can probably answer two of your questions.

1. The MV seat (which is on both the Weekender and MV) will fit in the back.
You will also need the rear deck (including the cabinets, supports and rear
pad) that goes behind the seat as it forms part of the bed.

2. The middle seat gets in the way when the rear seat folds down. The MV and
weekender have rear facing seats which fold up and out of the way when the
rear seat is folded forward. I guess your option is to remove the middle
seat any time you are going camping. Forget about adding the MV mid. seats as
you will have to find the front seat platforms so that the folding seats
can lock into place.

Overall, you would be better off trying ot find an MV.

Ric