Bits & Pieces:

Spesh 2Bliss tyres
DT Swiss 420SL rims with blue 'specialized rim tape'
Specialized sealant (it was all they had in the shop)
valves
Track Pump

I took the tube out of the wheel, stuck the valve in & thought I'd see if the tyre inflated OK as it was….and it did. Wahoo, this is easy, I thought. Air was leaking, but seating the tyre & inflating it seemed to be possible.
Air was leaking from the valve, so I tightened the lockring on the valve until it sealed (concious not to pull it all the way through).
This worked and so I put the sealant in…..but, now the air is seeping out of the spoke nipples…..I tried for ages to get it all to seal, but it wasn't having any of it so i gave up & stopped for some beers…..

The next day I had a proper look at the rim tape and it looks like it's not been put on very well, as it comes very close to the holes in places (i should have checked this to start).
I found some pics online of Spesh wheels with this rim tape & it was right up to the inside edge of the rim all the way round so suspect this is my problem. There were various forums saying that their tyres went up & stayed up no problem with 2Bliss tyres and this 'blue rim tape'.

The plan now is to get some of the stans yellow rim tape, but what width should I go for? It looks to me that 25mm will be too wide for the rim & will extend right up the inside edge, but i am concerned that 21mm will be too narrow. I thought I'd go for 21mm & run it round 1 edge, then run it again around the opposite edge if it is slightly too narrow.
On the sealant front, is the Spesh stuff any good? It is much gloopier than i thought and seems to have spread itself around the tyre in uneven globs. Is this because I've not actually ridden the tyre to get it properly sloshed around? Is the Stan's stuff better??

I was hoping to have this tried & tested before I go to Spain in a few weeks, but I am runnig out of time to get it done…..

I had trouble with air leaking from the valve on a proper ust rim and tyre. Tightened the lockring then it started leaking from spoke holes. Pretty sure it was due to some wear around the valve hole on the rim (old rim) tightening the lockring just stopped it leaking out from there, the air just diverted through the rim and out of various spoke holes. I got a bit of ptfe tape, folded it over a few times then made a hole in it, pushed the valve trhough then refitted it to rim, sorted it out.

no idea about the other Qs you ask but just a word of caution, I tried regular tyres with sealent and trashed them even at over 30psi, sidewalls are too flimsy, UST with a lot more rubber in the sidewalls fair better. Might not be a problem at home but if you're going somewhere rocky in spain….

electrical insulation tape.

2nd peachos, was suprised how well this actually worked, and damn site cheaper

You need more than one turn of tape on those rims to seal the holes, they're not designed to be run tubeless just with the tape. Electrical tape will certainly be cheaper.

Cheers – I did think about electrical tape, but didn't wanna rip off the current rim tape before asking for some advice. Will try that instead.

Donk – good idea about the ptfe tape to seal around the valve. Think I'll try that too.
I was a bit concerned about tyre durability, but I generally mince over most stuff & don't get my tyres off the ground (on purpose) so I 'should' be ok! Famous last words I know….

njee20 – it looks like the tape has been put round a couple of times, but just really badly. Some sections it sits really well across the whole rim and other areas it's almost falling into the holes.

Will the sealant be OK sat in the tyre for a couple of days without a rim, or will it start to harden up? Should I clean it out & start afresh? Wish I'd got round to this a month ago!

Its the specialized sealant, almost certainly, have tried it on my stans setup once an it is the only variety that won't seal….

borwens – I have heard that before, which is why I asked the question……think I'll get some of the stans stuff.