Swingout extensions?

The strain with extensions was the first thing I thought of. My other issue is that my tires barely, just barely, clear whatever I have the jacks sitting on, usually a 2" concrete block.
If I could get just another 1" clearance, I would breathe easier.

I had about 3/4" clearance each side on mine with brackets. It was enough for me for 7 years. I wouldn't want to put any more stress on those mounts. The attachment is weak anyway.

The swingout extensions on my Bigfoot were not enough to clear the fenders on my dually so I made extensions out of 4" channel iron. That was 8 years ago and they've worked out perfectly.

3/4" is plenty :). That is about what I have. On my previous truck and camper (F350Dually and 1996 BigFoot 25C9.4), the Happijack swingouts were insufficient for any clearance. I made extensions, by bolting a piece of 2 x 2 steel tube between the jack mount and the swingout bracket. My concern was that the further out the jacks are, the more torque is put on the jack mounts, trying to twist them off. They are not well designed to resist this kind of load. The stock swingout puts them out about 6" or so, adding 5" will nearly double that offset torque.

On my extensions, I welded 1" tube across the camper from one extension to the other, so that the offset torque was resolved between the two extensions and not transmitted to the camper jack mounts. It worked without problems for 15 years when I sold the camper to someone with singles, and he took it off.