XM radio installation help

I've got an older model XM radio. I've installed it in the top case on my 2013 RT. It works fairly well, but I have an issue.

Since my radio is an older model and no longer available, I can't get a car kit for it. The only way to get an antenna to it is to install the radio into a base. I have the base velcro'd to the shelf at the back of the case and I have taped the radio and base together to keep it seated.

I problem is that it shuts itself off at times. I think a bump in the road is interrupting the connection momentarily since the power is also provided from the base. I might try sitting the base inside the case on a cushion of sorts to see if that helps.

Does anyone know of an XM radio currently available that will allow antenna and power to be attached without a base? I'd be willing to transfer my XM subscription if I can find one.