OK. Good one Richard.
Re carpet I'm no expert that's for sure. I actually left the underside of my base bare so that the ribbing of the decking that I used to increase the height provides a little extra lateral grip. Mine is only fixed by the tiedown bolts on one side and straps in the centre so not as well anchored as yours will be with 4 bolts through it.
http://www.aulro.com/afvb/attachment...1&d=1425341075
I used carpet from Bunnings fixed with liquid nails - seems to grab quite quickly and looks ok. The carpet is a surprisingly good match. Cutting the carpet at the corners is tricky though.
http://www.aulro.com/afvb/attachment...1&d=1425341288
http://www.aulro.com/afvb/attachment...1&d=1425341288
The little hols I cut out are for the bolts to go through freely to the captive t-nuts on the under side. I like those as I think they provide a stronger fixing than screws and you don't need access to them as you would with a nut on the underside.
I'll be interested to see photos of your project as it progresses.
Cheers,
David