I say Why Not!!! However, I'd keep in mind the set up and take down that you'll be incorporating. The "hobby killer" for a lot of people is the never ending monotony of "getting ready" to do
AP. The other issue, and you touched on it, is the weight of the new combination. While the mount will handle the extra burden, we as people are always getting older, and may eventually not be able to handle the weight of moving the thing at set-up/take down.
My point may be moot if you don't have to do anything too extraneous to do the
AP you want to do. For me to make a logical, helpful analysis I'd need a wee bit more info on what you are using now. Are you using a pier or tripod, you mention a "permanent fixed site", please explain. Do you have to strip part of your rig down every time you use it to prevent the climate for wrecking something? Scotland does have a rep for it's climate....
While I mostly do
DSO AP I do when the opportunity arises do a bit of WL Solar imaging. A used C8 I bought came with some goodies that make that possible. My current set-up allows me to put everything I need together in less than 10 minutes, and if I have to hustle to break it down (ie. freak thunderstorm) it can happen in about 4 minutes. However, I have the
AP bug bad!!! I have chased opportunities through "sucker holes" in the clouds day or night!
In the end if you know your mount will handle the extra burden, and it makes you happy adding another scope to the WO do it. I too have done this, and it was on the cheap, I have built my own brackets for a few different things. But most into Astronomy don't have the pack-rat syndrome I have or the shop to make it all happen.
Scopes: SkyWatcher 8" Quattro, Celestron C8, SkyWatcher ST120, Orion ST80, SharpStar 61EDPH II. SLT 130 Celestron
Mounts: CGEM, CG-4, EQ2, Alt Az, SLT
Cameras: ZWO ASI533MC Pro, ZWO ASI120MM, Canon 1100D