Wet ground (Scotish Highlands) without a bathtub?

You can easily enough find dryish ground in Scotland; so a bivvy or just Polycryo can suffice (obviously you need to choose your pitch). I've camped extensively in the Cairngorms and less so in the Western highlands.

In my limited experience in Scotland (western Highlands, Skye) I believe that a bathtub floor might not be necessary but would give you more flexibility in choosing campsites. IMO, the small weight increase is worth the added flexibility. Keepin midges out of your sleeping quarters is pretty important BTW.

We usually managed to find somewhere better drained. Camping in mud or bog … not my cup of tea. Cheers

The camping options are pretty good :-)

The valleys in the West and North West Highlands are either boggy or tussocky or both. Higher up on ridges etc is rocky and dryier but more exposed. Good pitches can be found but it takes luck or prior knowledge. Also be aware that midges and ticks live in the undergrowth, altho' less of an issue in spring. You won't give a fig about UL if you are being eaten by midges! I always use a fully enclosed inner or single skin with bathtub floor.