Hi there ! I'm happy to see an other sun RMT which is not very common at all so thanks for doing it ^^
First of all, I would like to talk about this Tran and sun in general. Since Solar beam + sunny day on tailes and MagmaTran were well known today by many players it was not so easy to trap all the weather inducers at the end of BW 1. I also find out and tried this Tran with a similar spread some monthes ago. Sure it is nice for trapping Politoed ( The defensive one ), it also provides the sun when needed and can still trap Hipodown ( air balloon have already been sugested so yes ) and Tyranitar. But the fact is that you can carry "only" one steel type in a sun team which is most of the time Heatran and this one can't check 2 Dragoons attack because of its spread. Plus it doesn't have Earth Power which is extremly important in order to deal with other Tran which is always painfull for a sun team.
Considering your team and what you wrote on the threat list it seems all good but considering opponent's "standard " teams it's not at all, why?
You said Dugtrio take care of Tyra but Also Tran and Volcarona and Bliss, Politoead, etc. However, dug also has to put Sealth rocks on the battlefield and the problem is that for example most of the sand have Tyra + Heatran, sun: Volca + Tran etc.
Concerning Dugtrio, it is the key for many sun team same for yours. But it is also a huge weakness since first you totally depend of it, plus, Pokemon which are able to set up enjoy coming on him. Dragonite, Gyarados, Gliscor( who is not in the T list), SDZor etc. etc.
They are all huge threat since we both know that Heatran will not have the balloon when this situation will happen. No sun yet, not sure to have SR but you just won the weather war and then?
If Dragonite has extrem speed you will lost Dug, Tailes and Victree will have a chance to die after the LO damage recoil.
Gyarados ( if not sr ) is not dead after a rock slide ( the moxie one ) and a Giga drain. DD on Dug and then 1 kill, it is at +2 more than 50% of its life Hydreigon can't take a bounce.
Gliscor Sub, you will sack tailes for sun and then?
Scizor will be a late game sweeper since as you said it has nothing to do against a tailes or Tran but he is able to stop your Victreesweep doing between 75 and 90% with BP.
All those threats are in green or are not even present in the T list :(
Concerning the suggestions:
Harsha already tell you about Duggy but I may add something else. I think Rock Tomb is the best move for Dug in this team instead of Rock slide. In fact what I said earlier was also true for my team long time ago and after checking his moveset I finally found this greeeeeeat move :d
Rock tomb is only 80% accurency and has "only " 50 power, yes but it still OHKO the offensive version of Volca and do not let the bulky version set up his speed. Same for the other Pokemon. then it means that Heatran, Hydreigon, Victreebel can still outspeed those Pokemon. Same for Gliscor, you rock tomb the acrobatics version and you will outspeed him with all your Pokemon. And to conclude, if you are facing a Choice scarf Politoad but you didn't know so you trapped it with magma on the switch but kill you with hydro. Then dug, Rock tomb, you outseed him now and you have 1%, reversal GG.
After this, I can't really suggest you to change your heatran or something but I really do not aprove the choice of Starmie... Same for Claydol. Starmie is a spiner ok but without HP fire, Ice beam or Thunderbolt... It is useless in the team. Pokemon can set up on him, Jellicent walls him, Ferothorn too and may paralyse a member of the team.
Who is your lead when there is a Landorus in the oposite team now? Well I don't know what to say... Otherwise you need EP or Focus Blast on Hydreigon for Tran.
I can't say more right now I guess... Hope I helped and sorry if I talked like if I was knowing all about Poke lol It is just that I have a similar team and did a tone of matches with it...