Hatman-I have precicely the dual-voltage system you envision...
A 2006 Jayco 29' Travel Trailer with both 110v and 12v circuitry, hookup to campground power and battery backup with built-in inverter. All I need to do is expand my battery pack from 1 to say, 6, add some Solar panels and go nuts on closed foam insulation, and i'm set-assuming the campground gives me the go-ahead to set up a stationary solar bank at the angle I want...also, the Propane heater array has this beautiful intake vent that will allow me to plug in one of my Soup Can Solar Thermal units directly into the existing heating ducts...
{What I will NOT have is the ability to sell back power-campgrounds just don't DO that. Also, I need to create another Soup Can Unit-the couple I sold my three bedroom, two bath house to were so impressed by my winter power usage they asked me to leave my mods (triple-wrapped pipes, dual Soup Can Units and bubble wrap on the already state-of-the-art windows...total cost of under $80 ) I recommended they visit this Forum of course...}
As to Grid-tie systems in general...i'm not impressed. Several neighbors (well former neighbors as of two weeks ago) spent roughly $40,000+ on the Grid-tie system, and while there was some reduction, the 'progressive' metering system of the Co-op meant that they paid more per KWH, much as I did with my more modest Eco-mods.In addition, they still lost power during a blackout. Two of my neighbors eventually upgraded an extra $20,000 in panels in order to push thier bills into modest returns-which won't pay for itself for nearly 18 years...my other neighbor spent an extra $35,000 to convert into a fully off-grid facility-she won't see a real profit either but feels beter knowing she can play host to her street in a emergency.
If I were going for an independent dual system like the one you described Hatman-i'd most likely try to place a few of my most vital system (say, fridge/freezer, water pump if you have a well, one string of lights, one 'special outlet' for a single 110/120V directly to the battery pack for one or two emergency plug-ins like electric heaters and a hot plate) on dual switches. If you could run a single circuit through a few vital systems-with switches to move those facilities from circuit A to circuit B-that would probably be the least invasive(and least expensive) approach. My new (to me) RV simply switches everything at once to battery if the power goes out-which is fine for a relatively small dwelling, but my refrigerator has a manual setting for triple use-Mains, Battery and Propane-which sort of illustrates what i'm rambling about...
I assume that you've already checked the guidelines in your State to see if you're allowed to do this (NC guidelines are one of the many reasons I sold my house in the first place-I do NOT like being told what I can do with my own property!!!). Failing that, I'm assuming you'll have the skillset you need to do the job yourself...best of luck.
BTW Ford Man-I love the idea of a 'safe' Kerosene heater, this is the first i've heard of it. I had a heater myself in case of winter blackout in my former home, but I dreaded the fumes...I would have had a woodstove myself but I wasn't willing to blow $7000+ on an electric fan insert, and NC wouldn't sign off on my $20 hand-made unit no matter how many times thier OWN INSPECTOR signed off the Safety Approval (yes my little feud has long-term roots...). Not to derail this Thread, but i'm curious as to your layout...do you have plenty of room facing the South, with two or more windows and room for some Thermal Mass tanks , either sand or water based? PM me, I may have some cheap ideas for you, and if you think they're worth it we'll start a different thread ( HINT: it involves Soupcan Thermal and transmission through coils snaking through Thermal Mass storage...)