Re: hf radio modified marine or modified ham
"if I wanted a low cost radio capable of "
Yeah, skip the big radio there's no such thing as a cheap one.
Buy a CB for the truck, a VHF for the boat, and a PLB to use in real emergencies wherever you happen to be, in case one of those doesn't get you help. All three of those combined will be cheaper than the option.
For a legal combination ham/ marine-ssb rig you'll pay a fast thousand bucks before you starting the installation. And it won't be terribly portable to fit most vehicles. And then of course, you'll need the licenses (ham, ships, ship operators) as well.