I would get a good quality extension cord. Perhaps a 10Gauge (10-3) contractor grade.
The red-orange cords from WALMART just won't hack it...
Also I never have any luck with those small round black adapters... The only thing that really works is the RV30A-15A LONG dog bone style adapters. You can pick these up at WALMART back in the camping section items...
The 30A RV30-15 looks like this...
They also have the 50A to 30A long adapter then you use the 30A-15A to get all of that down to the garage 120VAC receptacle.
You also have to watch what you plug into in the house... Make sure the 120VAC receptacle is wired correctly using one of these circuit testers...
Keep in mind the trailer requires all three of the conductors to be used when plugged in. This is where the trailer safety frame ground comes from. Some folks will cut the ground pin off of an extension cord for whatever reason. Trailer has to use all three conductors.
I also have one of these RV120VAC meters plugged into the trailer where i can see it easily. This one has the GREEN safe zone printed on the scale. I will not turn on my Air Conditioner or high wattage microwave etc unless the 120VAC coming from the house is within the GREEN safe zone...
Roy Ken