Instead of fiddling around with your H25, why don't you just purchase (used) an old compatible SD receiver and add it to your account (for $6/mo) and take it up to camp? I'm sure those brainy CSR's would have no clue that it wouldn't work with your SWM dish and would cheerfully add it to your account.
Irregardless if you transport your H25 to camp or do the above you are in violation of the Terms of Service since all receivers on an account are supposed to be at the same address.
Sigh. Taking a receiver camping with you is fine. Having three receivers at one house, three at another, all active on one account at the same time is not.
A used receiver is probably the best way to go. *BUT* BE SURE TO CALL DIRECTV AND GIVE THEM THE RID BEFORE ANY MONEY CHANGES HANDS!
That way you'll know if you can indeed activate it on your account. A lot of people will try to sell their leased receivers after they cancel DirecTV and they even have balances left on their account, so this is why you must call DirecTV and verify that the receiver is owned/transferrable before you pay for it.
Once you buy a receiver and verify the RID you will need to buy an Access Card for $20. The Access Card team are the ones you really need to talk to, because they have the final say over whether they will allow a receiver to be on your account. A D12 will be no problem, a D10 or a D11 they may question you about but if you explain to them you are using it for camping it should not be an issue.
TL;DR: Buy a used SD receiver. Verify the RID with DirecTV. Much easier than having a full SWM-8 multiswitch just for camping.