I know Cardiff Ajax did something similar but under their own steam with a support van. If you think about the math, £100 per rider x 5 £500 (imagine what you could do with that!). You could simply look to rent or insure someone in a club members van for a couple of days who could provide food/drink/shelter as you ride plus make it more personal. Why not end in Saundersfoot rather than Chepstow?
Just a thought, I’ll go back under my rock now.