OK. You are new to this technology, which is fine, but there are a few basics that need to be covered. An LNB has to point (via a magnifying reflective dish) directly at the satellite that is producing the signal. You are dealing with a weak microwave signal at this point that cannot move over a cable. It is the LNB's job to convert that microwave signal to something in a lower frequency range that can be carried over coax. So, the LNB cannot be "in-line" with anything. It has to have a clear view of the incoming signal.
Your KVM dish is only large enough to concentrate the signal from one satellite (which in DirecTV's case is 101). At most the LNB inside the dome has two cable connections on it. Moreover, the aiming computer used in the KVH setup needs to have a signal from your single LNB to do the dish aiming. It would be totally confused if it saw a SWM signal. So, modifying anything associated with the KVM setup (without total replacement) is really out of the question. (While I am not sure, I also doubt you could put a SWM-8 switch downline in the coax since those units seem to want four inputs to work.) Since your KVH dome is only capable of seeing sat 101 you would be limited to standard definition on your reception.
I know you say you are satisfied with standard def from the H25, but a D12 receiver is just not that much bigger than the H25 and it would make you life so much easier. Yes, I know you said you have already purchased/leased the H25 but you would be so much better off to find a use for it in your house.
Or, you can do what I did and just skip the existing dish and do a tripod setup when you stop. In my case I had a Datron dish that the company quit the satellite business and left no upgrade path. I was not interested in spending the $1,600 or so it would cost for a new dish and bought the tripod, slimline dish, meter, PI and do my own setup. I just take the HR24 out of the bedroom and take it along with us on trips. It fits in the overhead compartment above the windshield and I use an rf box to drive the SD receiver in the bedroom. With an HR on the road you can watch whatever show you want at whatever time you want. I would really miss that capability with a standard receiver.
I hope I am clarifying things here and not adding more confusion.
Bob