I faced the same issue since just acquiring a new SPF, and put nearly 600 miles on it in three days, some highway and some back roads. It was well splattered here in OHio this time of years the bugs are thick and road kill plentiful. the first time I used the bucket and Zymol car wash with a large sponge, First using the hose to rinse any dust dirt away, then using the sponge soapy water , then clear low pressure rinse with th e hose and drying it with a
synthetic chamois, , results good, but got some water into the interior. The next time I took it to a hand car wash, put the tonneau cover in place and washed it being careful not to spray up under the tonneau. Dryed it with the chamois, and it all worked quite well with very little water getting to the interior. I do have a California duster for light maintenance, but when it get s really dusty I like the idea of using a hose to flow the dirt off before using a sponge on it, I intend to use Zaino brothers on it shortly.
And that's my $.02 worth