Living primarily in the desert Southwest, we do not use fenders/mudguards.
Having a trunkbag on rear rack does help the stoker in the rare case it does rain and avoids the rooster- tail marks on clothing. Pilot just puts with it.
Have been caught in few heavy downpours on tours. Once coming from Grand Canyon's South Rim to Flagstaff it rained buckets. About 60 miles at 7,000 ft. elevation and no place to hide anywhere! Did put on our rain jackets and pedaled on. Worst was vehicles spraying us with sheets of water as they blasted past at 60 mph. Fenders would not have made one iota of difference. We actually laughed about it and threatened to drill holes in bottom of our shoes just to let water out!
Deluge finally let up as we neared Flagstaff; stopped at a pancake house in town to grab a bite. Waitress took pity on us and told us to put tandem in the lobby! Then brought us hot cofee and free pie!
Have also been caught, in the desert, in a horrendous hail storm. Again we were on a tour and saw a huge blackness in front of us. Stopped, and by the time we got out our rain jacket we got pelted by big hailstones. Stoker Kay was dancing around hollering "ouch, ouch!" as she put on her jacket. Temp dropped about 20 degrees, instantly so kept on the jackets.
After we hit our destination she found out her arms/legs had black and blue marks from the hail. All this stuff about 'it's a dry heat' in the desert is true, but not 100% of the time!
Did have half-fenders way back in 1975 on our Follis tandem, but then we lived inMichigan where rain was more likely.
We have so much sunshine out here that if it rains, we don't go riding. There's always 'manana'!
Pedal on TWOgether!
Rudy and Kay/zonatandem