eventually will be getting round to the body work on Gunther (as he has now been christened) after slowly resolving the long running engine saga

Van (Autosleeper Trident) needs a mix of spot repairs and some panel work (o/s sill, n/s/r wheel arch etc)

The plan is to re-paint the whole van in Celly but as it is too tall to fit in my workshop (who chose a hi-top

I will need to do the work outside over the spring (have looked at 2K but haven't got 2nd compressor for air fed mask and don't fancy the H&S issues)
Intention is to do all the prep work then apply paint over a coupe of (warm, non windy, dust free) days - ha!
So, thats the background - question really is, as I work around the van doing spot repairs and some panel work i want to be able to leave the repaired part in primer until the whole van is ready for paint. So wondered what is the best primer to use for the following situations....
welded repair, bare metal with original paint surrounding repaired area.
Spot repair, sanded back to bare metal with original paint surrounding repared area.
Basically want something that wont let moisture through to rust out the new metal and will be a good base for filler/stopper prior to celly basecoat/laquer.
Or am i talking rubbish (loads of mechanical experience, long time since I did paint

Cheers,
MM