I'm not really sure, since you're running both a Venusaur and a Sawsbuck, a fire absorber is an absolute necessity. Tails and Darmanitan just don't have the bulk to take fire attacks, Kingdra just doesn't fit with a sun team.
Common options for the designated fire absorber are, take your pick and it should be easy to build from there:
Heatran
Dragonite
Latias
Vaporeon (for its wish support but its a liability offensively, so I'd suggest against it)
Chandelure
Arcanine