This is what we do... I just connect my trailer 30AMP shore Power Cable directly to the 2KW Honda Generator 120VAC receptacle using the proper RV30A-15A long adapter (WALMART) Looks like this
If your 30AMP trailer is equipped with a smart-mode technology converter/charger unit then this will re-charge your trailer battery back up to its 90% charge state in as little as three hours generator run time. Not having the smart-mode charging type on-board converter/charger then it may take as much as 12 hours or so to re-charge your battery. If this is the case then its best to bring along a smart-mode portable charger unit like the B&D VEC1093DBD 40AMP Battery Charger and run that from the 2KW Honda Generator and connect the cables directly to the battery terminals. This too will will re-charge your battery in as little as three hours generator run time.
We camp all the time back off the power grid with our setup and our battery bank has 255AHs capacity. We can run all the 120VAC items we want to have from an Inverter and all the 12VDC items direct connected to the battery bank we want to run and have planned it drain down our to around 12.0VDC by 8AM the next morning. This is when we want to re-charge our battery bank back up to its 90% charge state so we can do all of this all over again for the next day/night camping off the batteries. We can do around two weeks of this 50% to 90% recharge cycles without doing harm to our batteries but have to charge them up to their 100% charge state after about 14 charge cycles or so otherwise we will start doing damage to our batteries.
Been camping off the power grid using this method for around five years now and my three 85AH standard Issue Interstate GP24 batteries are just now needing replaced. We load down our batteries with around 20AMPS drain for four hours or so everynight with an parasitic drain of around 1AMP or so for the rest of the time. This drops our batteries down to around 12.0VDC (approximately 50% charge state) at 8AM each morning. Get to watch NCIS and CSI everynight using our OTA Batwing antenna before lights out.
It does take some planning and some battery savings ideas like LED lights and adding smart-mode charging technology converter/charger units etc...
Only way to camp for us....