I'm putting together a radio set-up I can take up to some local mountains, and want to know how I would need to modify my call-sign. I would be approx. 25 miles from my house.
It's advised that you identify as WF7BSR/P (on voice "whiskey foxtrot seven bravo sierra romeo stroke portable"). Some countires require the /P, while in others it's optional.
More people will want to work you if you're portable, and in case SOTA chasers aren't sure if you're on the summit or operating from home the /P should make it clear that you're actually on a summit or otherwise away from your fixed home station.
If you're using less than 5 watts, you might want to use /P/QRP, but many QRP operators just use /P. Some use /QRP if they're running low power from home, while some never use the /QRP suffix.
And how would I indicate this new location when sending logs to LoTW...would I need to get a new Certificate for that location? I would not be operating from a vehicle, but a fixed position.
If you're using off-grid power (battery, solar) and portable antennas, you're still considered a portable station - not fixed. (If you can move the station while operating you're /M in a car, /PM on foot, /MM on the open sea, /M on an inland lake, and /AM in a airplane.)
You would need a second certificate for the /P, but you can do that all online since your non-portable callsign is already approved. No more waiting for postal mail.
Also, you create as many new operating locations within tqsl as you like - you don't need new certificates for each operating location, just for each new callsign and suffix. You end up with a list like
WF7BSR - home
WF7BSR/P - summit 1 and 2
WF7BSR/P - summit 3
WF7BSR/P - city park
In this list summit 1 and 2 are in the same grid square (and zones) so I treat it as the same location.