Much though I like 4 PARA, a 280 mile round trip sounds excessive.
The Commando Gunners in Bristol were a good unit, I am out of date on what they are doing now but they would be worth a look.
If you insist on joining 4 PARA it might still be an idea to get the basics sorted in a local unit and then transfer to 4 PARA. If you get a good recommendation from you local unit you should be able to skip most of the Tuesday nights and just do the weekends.
As I understand it you might be most comfortably placed within pre-breakfast running distance, allowing time to stop to call the emergency services should you ever come across a suspected burglar who has fallen down a well
Over here in the land of Oz, the Army Reserves, equivalent to TA, the similar situation as yours does occur and on a greater distance. 2 Commando Coy, 1st Commando Regiment, which is based in a suburb of Melbourne, Williamstown, there were soldiers coming from Albury/Wadonga which is just a bit over 300 k's away. They used to come down on the Tuesday, after parade get a few hours kip at the drill hall then drive back. Same with 1 Commando Coy, 1st Commando Regiment, which are based in Mosman, Sydney, there were guys travelling up from Canberra, ACT a trip of around 300 k's.
I guess the moral in this tale is how's your commitment? I won't go into the differences between Oz/UK transport, because I cannot comment on the UK system, just as I stated, your commitment, and ways to get around the tyranny of distance.