DG: you are correct; it is very difficult to trim in a turn, and why would you? 180 degrees takes 60-90secs depending on speed. Not too long to hold with your leg. If you feel you have too - there is Never & Should Not & Not Recommended - from the sim exercises I've done for decades the trim settings are noted. If stable on thrust & speed at Up - F15 the zero force trim setting is 4-5 units. If at climb power stable speed it is 9-10.
When trimming, PM can set it for you on command, or you can time it. The trim rate is 1 unit/2secs. So you can set it with eyes still on EFIS and then check it after X secs with a glance.
I endorse the 'should not' in a turn, for trim & flaps.