We have tried several types of towing mirrors with varying rates of success. When we sold our last van, I gave my mirrors away with the deal. Now getting back into caravanning, we bought a pair of 'Cipa Custom Slide Over' Towing Mirrors online from the USA. These mirrors completely slide over your existing mirror and make it look like a 'one-piece' assembly. There are no rubber straps, no suction caps, no magnets to attach, no support rods, etc. The slide over mirror attaches with a wedge-like clamp set-up that is really secure and hidden when the mirror is installed.
They are available in the US for various US makes and models like Toyota, Jeep Cherokee and Ford Ranger. If you are lucky some of the US models available are the exact same our local vehicles here. We ordered ours from the US on eBay as I haven't seen any place in Australia that stocks them. As we couldn't find the current Prado to be available, we took the gamble and bought a pair that are made for the Toyota Tundra. There are some dimensions supplied on the website.
The Toyota Tundra Mirrors fit the 150 Prado about 95%, but even at 95% they fit a lot better than other mirrors we have used before and at around $100 delivered here, we can't complain. Also with a slight modification to the (plastic) attachment clamp wedge, that can be made to fit even better. The Cipa US website is:
http://www.cipausa.com/product/custom-towing-mirrors-11300
Just do a search in eBay for 'Cipa towing mirrors'.