We did used the entire 48" receiver and it was welded to the first cross member on the frame. It tows perfect, I've had it up to 70 mph around here and my brother had it up to 80 mph bringing it back here with no issues. The trailr tracks great, no bouncing and you can barely see it in either mirror when towing. As far as positives / negatives to the length, my tongue length was dictated by the need to be able to carry 12 ft kayaks on top of the trailer and not have issues with clearance in the front. I'm using a max coupler on mine also. I'll let my brother comment about any tricks or tips to getting the tongue straight and level since he took care of that part of it. Hope this helps you out.
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It's a cell phone shot but it makes the point of the clearance that I need.