Hey, what a lot of questions! Or rather, what a lot of related points you raise.
Consider giving your GF a break and budget for a night or two with a solid roof over your heads, especially when it has been raining during the day.
You can stop riding a bit earlier than usual and shop around for the best bargains - I've done that on the mile or so of B&B places on the south side of Fort William. Think of it as just an additional cost, over and above that for a camp site. It being June, you are outside the school hols season.
For me, I would just get some Ortlieb type dry bags and bungie them to your hard luggage for the camping kit.
As for Scotland, it is bigger than is often appreciated if you haven't been there before - head for the West coast and take it as it comes; you can do 250 miles per day and still be just up the coast from where you departed that morning.
by the way!
Last edited by Bertrand; 3 Feb 2012 at 16:24.
Reason: tidied up as quote mixed in response