I used to do trips like this years ago, nowadays I have learnt if you use a bit of nous there really is no need to do bad weather.
This weekend we looked at the forecast and went to the Dales that weekend, twas brill.
Over the years I have played the wet weather game many times and learnt more than a few lessons so here are a few tips.
1/Don't blindly book expensive accomodation way in advance coz you have idea what the weather will be doing on the day.
A great alternative is to join one of the major mountaineering clubs that give access to a network of accomodation across every mountain area in the UK without having to book weeks in advance.
My tip is to fix a date for a trip then ring round the group 24hrs before before and decide the venue, pending the weather.
There is a choice of last minute accomodation in Cornwall,South Wales, North Wales, Peak, Dales, Lakes, several areas of Scotland, its rarely wet everywhere in the UK.
You cannot control the weather BUT this way you can pick the best of what is on offer.
Plus its a fraction of the cost of a YHA so your onto a win/win...........
2/If you do get caught with bad weather in Glencoe, stay low, In the past when faced with situations like this I have found the solution to be the coast, check the map of the Glencoe area of Scotland, it has dozens of mini peninsula’s all of them are potential coastal walks.
My favorite is to take the Coran ferry and head south. Look for a blister of land jutting out into the sea. It gives a great day out stunning scenary with optional scrambling, very similar to the Aonach Eagach, there is even a bothy half way to have your lunch in..........
3/The Balachullish Horseshoe is a tough walk cos it starts at almost sea level (most munros are tough compared to english/welsh hills).
The best/easiest/safest wet weather Munro in Glencoe is Aonach Beag, cos its a roadside hill, good paths and you start walking from the top of a pass, well worth saving this one for a wet day...........
4/You will drive past some superb hills on the way too and back from Glencoe that may be dryer than your final venue.
Over the years many wet Scottish Sundays have been saved by dry weather on the way home.
Contenders for this are Arrochar Alps, the little known Moffat area is superb, like Lake District hills perched next to the M74. Have even done things like Blencathra and Cross fell after being rained out of Scotland.
Even now when I travel to Scotland to do my Munros I normally bag a hill driving north and another one or sometimes two on the way home..........