30 amp TS in the main feed is fine. Low cost and simple. Do need to make sure the converter or battery charging system is turned off. Otherwise you create a power loop that will drain your battery fast.
Other issue is make sure air conditioner stays off and fridge and water are set to propane only.
Could also add small 15 or 20 amp transfer switch to just the branch circuits you need. Or a sub panel to only power what you connect.
Is this 300 watts for small stuff or 2000+ watts for microwave, coffee, toaster, hair dryer, etc? Need 4+ batteries for the large inverter.