Talk Morgan Forums Community The Malvern Arms Waterproof bag to contain suitcase on car rack/

can also try Lomo for dry bags have various sizes

http://www.lomo.co.uk/acatalog/Dry-Boxes-dry-bags-uk.html

An Ortlieb XL Rack Pack is a perfect fit on the luggage rack and secured by the end closure straps on the bag so no need for additional straps. Fully waterproof and lightweight. Can be paired with a 120 litre Pacsafe Backpack and Bag Protector to lock the bag to the rack. It may not look pretty but it’s functional and saves a lot of faffing about.

Just remembered looking at motorbike paniers clipped to lockable mounts on the rack.
Givi is a good make.
Not cheap though

I have used this approach, I have a pair of 35litre Givi Monokey panniers and a rack left over from my motorcycling days. It's easy to mount the rack, the pannier locks on very securely, and they are of course completely waterproof.

The big disadvantage from my point of view is that they obscure rearward vision more than I like, which is why I switched to a Peli case. Just as waterproof, lower profile, but the tradeoff is a smaller volume. Fine for a couple of nights, though. Any more and I use a soft leather holdall behind the seats.

That is the approach I use. Comments above re the cases sitting high are true. This year, I plan to adapt a John Worrall Low Line Luggage Rack. This way, I can make the pannnier bracket mounting more secure and also swap back to the rack with side screen stowage when not on a long touring holiday.

My purchase of a very nice Plus4 from Uncle Melvyn (Rutter) came complete with a suitcase bag that he supplied to the original owner, which is yet to be tested (by me) but looks the part. So I would suggest anyone interested contacts MR to investigate further

The only thing I ever foiund that did keep things completely dry was one of these http://www.marinesuperstore.com/clothing-accessories/luggage/gill-dry-cylinder-bag

I used the Aldi version on the back of my motorbike for going to the TT and camping there. Some days the rain was biblical and at 70 mph ( never more officer) it still kept the water out.

If anyone is interested in in this set up, I have exactly the same system that is no longer in use. It's a little battered in places but completely waterproof and secure. PM me and I can then sort out photos and a bargain price as it's just gathering dust at the moment.