Let me explain/clarify
I did research on bulb types that are fitted to my Airstream, and there are a few threads here on the forums that helped.
The Interior overhead lights mostly are called "1156" or "BA15s". This is the larger bayonette style bulb with a single center contact. In some of my overheads they have 2 different wattages, and the Spot/reading light bulbs are also 1156 style, but a spotlamp/focused bulb.
The 1156/BA15s is also the bulb used in the Reversing lights.
Some fitting have a small bodied "Twist in" style bulb with one center contact.... like the one I talk about above, but smaller... that is called a BA9s. My exterior upper marker lamps have 2 in each fitting.
The floor lights, outside marker, and Compartment lamps have the small push in bulbs, and these they call "Wedge" or T10..
Tail light bulbs are called 1157 or BAY15d..
This is a two contact bulb... Low and High brightness, for tail and brakelight.
This should help you find the right type of fitting, and narrow your searches!
Now, I look for bargains, and when i see them I buy them!
I look at the "Buy it now" only, and sort by lowest price..
This is where the deals are, but not all the time, so be patient!
You can also seach by the number of LED's.. Like 48 or 36 if you want LED panels...
Now, I have made some mistakes...
I got some 1156 bulbs for the interior.. these had 9 LED's mounted on the end...
Like these that were 99c for 2 with free shipping..
2pcs 9 LED 1156 Park Rear Stop Turn bulb light Bright | eBay
They fitted great and are bright, but I found this type of bulb is directional, and also very blue/white...
So were not good in the interior overheads, as the light is "Cold" and also focus the light wrongly.
I ended up putting those in the map reading lights, and they seem to work well.
I plan to try some like these "Warm White" side focus bulbs, but waiting for a better price...
1pcs BA15S 1156 1141 SMD bulb 13-5050 SMD LED,Warm White, DC12V, #13ZWW | eBay
The T10 bulbs I got are like these.. and at 99c for 2 inc shipping.
Not tried them yet, but I think they should work..
Super Bright White Light Bulb 12V T10 W5W 1 LED 1LED x2 | eBay
The Tail lamp bulbs I got are 1157 bulbs, with 102 SMD White LED's.
They are tall... but I measured and I think/hope they will fit!
Like these, but I paid $6.70/pair shipped..
1157 2057 T25 3528 102 SMD LED Car Brake Stop Tail Signal Light Lamp Bulb White | eBay
I will post pics and comment on my main thread when I try them!