A 30A system (3600 watts) is common and not bad but you have to manage power. For instance, likely will not be able to run a microwave, hair dryer or electric coffee maker and air conditioner at same time. Changing systems to 120V power systems decreases the power available to run other systems.
For 30A or 50A power you must be connected to shore power or generator. The 12V system uses batteries to power keeps lights, absorption fridge, hot water heater, AC thermostat etc.
As Kirk said... this is your RV, labor and money. Since you have gutted the 120V electrical system figured was a good time to
evaluate upgrading electrical system. Not necessary if you do not tax current 30A 3600W available.
Google - how to upgrade 30 amp to 50 amp
The following site appears to be informative:
In an era where RV travel is increasingly popular, ensuring your motorhome is equipped to handle modern electrical demands is paramount. In the article
e3camping.com
Jennifer