Just Soloed an Arcanine and here's what I thought
(For anyone who is interested in Soloing L3 Raid boss)
Conclusion:Vaporeon is the way to go. Not Golem. Haven't tried Rhydon, but I figured they perform similarly (RT being a slightly better quick attack while Rhydon having slightly higher ATK). Timing out is the issue, not fainting all Pokemon. Out of all Vapes WG/HP serves the best. Suggested powering Vapes to Lvl38+. Need 3+ of them, preferably 4. Details:
My squad was (in order) Lv37 RT/SE Golem, Lv39 WG/HP Vape, Lv39 WG/WP Vape and Lv 38.5 DT/O Dragonite. Arcanine was Fire Fang/Fire Blast.
No dodging. In the end, Golem and two Vapes died and Dragonite was left with about 1/4 of HP (see the pic below).
By the timer hit 135 (25% time passed) the Arcanine still had over 75% HP (so with Golem I was behind schedule), but the two Vapes speeded things up and, when the timer hits 45 (last 25% time), the Arcanine had less than 25% HP. Dragonite was just the filler, I would replace him with a high-level Vape if I had a third one.
Succeeded at my 2nd try. The first time it was super close but I had dodged twice with Golem. So I didn't dodge anything the 2nd time. The limit can still be pushed further (theoretically, 4 Lv40 WG/HP Vaporeon). Further discussion:
It is very expensive (stardust-wise) to solo an L3 Raid Boss. You need multiple copies of ultra-high level attackers. But it's one of the few things left that are challenging in this game! And the way I see it, this is the reason why they made it marginally doable to Lv38+ players (they tuned the numbers pretty well, I must say).
Therefore, my theory is, all L3 bosses are solo-able. I'll try to do all of them in the future to prove me wrong/right. Also, if you have soloed other Raid Boss, your sharing experiences is greatly welcome.
Cheers,
bioweapon

Answers
Sorry for not listing the IVs in the details. Here they are now. (IVs in ATK/DEF/STM)
Golem: 14/14/15, Level 37
Vaporeon #1 (WG/HP): 15/15/14, Level 39
Vaporeon #2 (WG/WP): 15/15/15, Level 39
Dragonite (DT/O): 14/15/15, Level 38.5.
Above Level 30, level still matters. The first time my Golem was at Level 33. Then I powered him up to Level 37 (my stardust is burning). Guessed that made about a second's difference!
I have soloed Machamp twice without much trouble.
Tried jolteon and couldn't do it. I have 2 level 30 ms/eq rhydon and one Golem, then used Dragonite DT/OR.
Dragonite actually seemed to do better, but I couldn't do it with various combinations. I'm level 38 and all I did was spam attack...no dodge
Really want to try an arcanine. I have 2 WG/HP vaps over level 30. One issue is if the Arcanine has Wild Charge the vaps are in trouble.
Nope. Just nope. You were lucky Arcanine didn't have wild charge. Rock / Ground reigns supreme unless you are certain Arcanine doesn't have wild charge. I previously solo'd Arcanine before and I used all Rhydon and Vaporeon. It wasn't really a walk in the park but I didn't find it super hard. Doing another solo run when I decided to roll with the same team. Unfortunately, Arcanine had Wild Charge. Wiped out my Vaporeons easily leaving me with 3 Rhydons.
Golem has higher cycle DPS than Vaporeon, although rounding issues might favor the faster quick attacks (in this case Watergun) a bit. I would recommend instead of wasting all your dust in 3 Vaporeons, power up different mons and then you have a diverse and flexible team. Btw, I am level 34 and soloed all Tier 3 except Jolteon & Flareon, so you don't have to bring them to lvl 38.
I tried a solo on an Arcanine on Monday. I got to the gym very late in the raid, with only about 18 minutes left.
I used Rhydon and Vapes. I timed out the first try with 4 Rhydon and 2 Vapes intermingled, and missed by about 8-10 %. What I did notice was that the Vapes WG/HP charged and hit faster than the Rhydon MS/SE.
I modified to 3 and 3 with the Rhydon and Vapes alternating and did a little better, but still timed out. I think I wasted time by dodging, and there was a lot of lag.
The 3rd try I went with 4 Vapes, but had to use 1 that had AT instead of HP. I ran the Vapes as the first 4, (Lost 3 of them, but never used the Rhydon.) then the 2 Rhydon. I still timed out, but this time with about 1 AT hit short of winning.
Gave up! (Was running out of potions/revives and the Raid timer was down to less than 1 minute.) But it convinced me:
A) Power up my Vapes with HP.
B) I can beat it if I get another chance
I also tried a solo on a Vape on Tuesday. It didn't go so well since I didn't have high enough Grass types.
I went in with 1 great Eggy, 1 so-so Eggy, 1 great Victreebel, and 3 nice but not the best Vileplume (All Vileplume level 20 - 22, used to be Prestigers). Got close, but couldn't seem to get over the hump. Luckily, after the 2nd failure, one other person ( level 27) showed up and gave it just enough damage to push us over the top. I've powered up the Grass types and want to try it again.
I'm also burning through the Dust. Went from slighlty over 2M on Monday morning to less than 1.5M today. Still have a bunch of other mon that I want to power up, so I'll probably be under 750K by the weekend.
BTW, I'm level 36.