You might try any of the several products made to clean motorcycles. I'm thinking of those that come in pump spray bottles. They help dissolve the bugs before a light washing. Bike Brite is the brand I have in my garage, though I've not tried it on my diamond plate yet. Warm soapy water has done it for me so far, but I don't tend to collect bugs on it because of the design of my tow vehicle.
It's never too late to have a happy childhood!
Lee, WU0V, and Courtenay, N0ZDT
2011 Rockwood A128
2000 Silverado 1500 pickup
60W solar system
2000W inverter generator