I have fdescussed thie onthis list and the other Airstream list previously. I am happy to add my 2 cents worth .
#1you are correct that it is best to drill a grid of holes about 3/16 in would be about right I would use a 11/2 grid I would use a stop block to prevent going all the way through.The ability to soak througr is some liminated depending on the condition and type of wood it will howeaver travle in the endgrain quite well du to capilarity action.
If the rot is near the edge of the trailer I would tilt the trailer slightly to insure that it goes into the channel and seals the end grin to prevent futher damage. If you have removed all the floor crovering I would pore pinitrating epoxy allthe way around the trailerso that you will seal the endgrain all the way around the trailer it is good insurance to prevent future rot which most generaly starts from water pinitrating unsealed endgrain. When pouring on the pinitrating epoxy watch it carefully and keep adding on the rotten aera until the wood will not asorb any more.
The treatment aftward depends how bad the floor is. I would at least craver the aera with a layer of fiberglass cloth. Rember that pinitrating epoxy is not to be used for laminating. Also it is not a cureall it has a limination but it has mabe our life a lot eaiser has made possable repairs that in the past were imnpossable.
Ouer engineering is better than underkill.
My advise is not to buy the trade names that are all over the country all brands of epoxies are basicly the same there are only a couple of manifacturs of epoxies.
Good luck
Jim Smith
1992 Tradewind(The Silver Abaltross)