Looking at the Soudatight LQ details online it seems it should be OK to use it in the corners (I think you have removed the coving?) as long as any cracks are fairly small (or filled before painting). I'd definitely use at least two coats of the paint as they suggest in the corners.

You could tape the corner if you wished. I would paint over the tape as well if you did this. When taping a corner you need to try to allow some slack across the width of the tape to accomodate any movement. That can be tricky to do. At a minimum ensure the tape is pushed right into the corner. Using a tape with a split backing makes it easier, but it is possible with a single backing if you are careful. Pressure sensitive adhesive is quite forgiving of being repositioned as long as it has just touched a surface and not been pressed/rolled into place.

You can buy Tescon Vana with split backing and in various widths depending on what you are most comfortable with. Maybe try to get a sample of each width if you are planning to tape the junction.

But having said all that I think a few coats of the paint should work well.

Posted By: GreenApprenticeThat tape looks like it will come in handy for lots of other tasks

We used quite a lot of it for most places. A few places we used various membranes (including DPM) where there were larger areas to cover (behind the ledger beams for the first floor joists and around the floor slab to wall junction come to mind) taped round the edges. Other places we used Contega tapes and Rissan where appropriate.