Selling and rebuying the mast sounds harder and more expensive than selling and rebuying the trailer. (and maybe harder than selling and rebuying the whole cat). Besides, the trailer could be useful later.
I carried a 27 feet mast on my Subaru Legacy roof once, but just a short distance
- Make sure to attach it at four points of the car not just one at the front and one at the rear.
- The bars of the rack are very close to each other in comparison to the lenght of the mast, so the tips of the mast will tend to move up and down. This means that the bars of the rack will support more load than just half of the weight of the mast. (if you apply a small force down at the tip of the mast, you will see how easy it is to bend the rack bars). Especially the front bar, because the mast will not be supported at the center, you want more mast length at the front than at the rear of the car.
- Tighten enough to avoid this up and down movement, the mast will bend. If you can manage to set it up with the diamonds on i think it would be better, but you need to avoid rotation of the mast and put a good cushion between the mast and the rack bar, because the area of contact is too small.
- Make sure both ends of the mast are VERY visible by other cars, not just a small red handkerchief.
- Don´t get distracted, especially on two way roads. On the curves the tip of the mast can visit the opposite lane.