Voltage in Travel Trailer

Voltage will often sag depending upon the load put on it, in both AC and DC circuits. Voltage sags both because power is being drained from the source and there is resistance to current flow within the power lines to the load.

I seems excessive to me. I would start checking the tightness of the wires in the breaker box. Then I would measure the voltage at the source power post, drop at he shore power end and etc.

You are looking for where the voltage drops when under load.

For example, if you have a long shore power cord that can do it, if so nothing is wrong, you just need a bigger gauge cord.

That is perfectly normal. As you draw additional current from the source, you increase the voltage drop in the feeder wires thus less at the outlets.

Mine varies between 110 to 124 volts depending on load. I think that is normal.

This isn't likely to be normal. It indicates a possible bad connection between 30 amp plug and pedestal; or a loose bad connection at the 30 amp breaker in the camper. Check the plug for indications of over heating, the same for the socket at the pedestal( that is up to the CG to fix the socket). With the shore power cable disconnected from the pedestal remove the cover from the distribution panel in the camper and inspect the connections to the 30 amp breaker and the neutral wire to the distribution panel. Since the distribution panel in the camper has 12 vdc you may want to disconnect your battery first. This is just for starters.