I have the same setup at home, but using the 3 network, and yes, the XPOL made a big difference. In the motorhome, I have a RUT955 and a Poynting Puck V1 antenna which have performed well - just the occasional spot in Scotland where the 3 signal was not usable, but there were some where there was no EE signal (to a phone, outside) but 3 was OK.I mounted a Poynting Xpol on the lift up pole for the TV aerial....
Made a big difference to reception (combined extra height and reception not being in a aluminium box)
Connected to a teltonika rut 950 with EE data sim means we, now have reception in places we previously didn't....
Fitting was easy enough IF your happy pfaffing with brackets and having to possibly adapt stuff for where you want to mount it...
Ohhh and possibly drilling/sealing holes to route the cable
You only require half the wave length, MI 1 DTI.Some external aerials require a ground plane, read device instruction, something to consider if the roof is fibreglass and not aluminium or steel.
A ~30x30cm piece of stainless sheets makes a nice ground plane improving aerial sensitivity.
You only require half the wave length, MI 1 DTI.