What is a good alternate port for Remote Desktop?

I have two computers that I would like to access remotely using Microsoft Remote Desktop. I have set up my router to forward port 3389 to the first computer and port 3390 (using the alternate port feature of Remote Desktop) to the second computer. I discovered on a recent trip that Marriot  hotels and Starbucks block outbound access on port 3390. Testing from a friends WiFi network with no outbound ports blocked everything works as expected.

I need to find a port that is not blocked by most public WiFi providers but won't interfere with normal operation while I am at home.

Any ideas?

Chip

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'I have yet to see any problem, however complicated, which, when looked at in the right way, did not become still more complicated.'