"Downside is that you need to maintain a £2000 or equivalent across both accounts. You can also set up a dollar savings account but interest rate is low 2.5% - but better than a shoe box."
That's not strictly true. You only have to have at least £2000 in any one of your accounts.
Also, you can have a sterling savings account which pays out around 5% and that can be used to transfer between USD and GBP as well.
That's the way I do it any way. I'm currently in the US and taking full advantage of it !!