AC refrigerant replacement

[Roger Scow <rscow@domain.elided>]

With summer coming, I think I'll need my AC more that I need an air
compressor...have one for the shop.

My R12 is long gone.  I suppose I'll need R134a or one of the other
alternative refrigerants.  Have any of you folks had any experience with
the changeover?  Do it yourself, or does this necessitate taking the rig
into an AC shop?   I'd like to get on this pretty soon.

Roger

'78 Traveler/392/727
***
It's funny, you'd think that all of those guys in MENSA, the genius club,
could have figured out that, in Spanish, "mensa" means "stupid."