jbad...a 473 is completely unsuitable for portable. Indeed...you will need somewhere over 20,000 Btu's and probably 2 units to keep the boat cool.
I would suggest a 16k unit for the main cabin and a 6k unit for the master stateroom.
You will need through hulls for the installation so will need to pull the boat.
The work is not at all hard and if you are reasonably handy, you can do it yourself. Lots of good companies...Marine Airr makes a fine product and offers good support among others.
This will not be cheap...but portable will be a waste of money in my opinion.
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