Did you try any of the following first:
Press reset breaker on Onan?
Press reset breaker on Tripp-Lite inverter charger?
Lightly tap the Intellitec battery disconnect just in case it was stuck?
Was it a relay or the automatic transfer switch that was replaced?
Your '06 would likely have had a 750W inverter/charger. Due to the design of the overall system, the inverter part was only meant to power things like a TV etc. and not the Microwave oven.
A light blowing a fuse would indicate a short I think or maybe a very loose connection causing high amperage. I'd first visually inspect the bulb socket and wires there. If you have to pay to get it fixed then do it - better to be safe than sorry. The fuse is a safety device and it would appear that it is doing its job.
You can get a sewer hose coupler - https://www.amazon.com/Camco-39203-I.../dp/B000BQYK6I
- to use with two large hose clamps if you have space for it.
The price you paid seems high but we don't know what parts were installed. I'm assuming you agreed to the loss of the inverter in your RV. I'd be quite upset if they took that away without my permission.
The TV was 120V AC in the Roadtrek I had - no inverter = no TV. I think Winnebago uses a 12V DC TV.