there are some typical areas on the mazdas which are prone to rusting like all other brand makes. rear boot lid with rear windscreen's lower channel is among them. among others are sills, front inner quarter panrels, front windscreen cowel panel, fresh air heater tunnels, A-pillar bases and radiator panels, to name a few.
i had these pella pics saved for a later point in time to show and discuss the rusting spots on the mazdas but since you have brought it up, i will post these here
front driver's side fresh air tunnel on pella
left one is not different either but it has received some repairs in the past as you can see there are two patches welded onto it
the inner quarter panels
as you could possibly see in the above pic, the pass side A-pillar shows signs of a hit/repair in past, this will be some serious structural repair when we come to this as it also has rendered the complete windscreen A-pillar crooked
radiator or headlights panel which i am replacing with a NOS panel
a clear pic of the driver's side fresh air tunnel showing the true extent of the rot
i have more pics taken of the windscreens' rot and cowel panel rot that i will post later. these are posted here just to show a few rust prone areas on the mazdas and trust me, its not just on the pellas its for all the mazdas