We would like to point you at two nice blogs from two tours of two Italian guys. One is called Good Biking Vietnam a tour powered by Vietnamese smiles and the other one is Riding around Gulf of Siam. The first tour was done in 2011 and the second one this year in spring.
The used two Challenge Seiran recumbents, made nice pictures and it seems they will also have some nice video sonner or later as they had a special holder for a camera on one of the bikes.
It is defientely worth to look at least on the pictures. Guys had definetely a good adventures there.