The dog must be made to feel at home in dog crate training.
When you crate train your dog do it slowly and with great care.
Crate training a puppy and a dog should follow similar stages.
If you know your older dog has been frightened before just take it much slower to build confidence.

1. Just have the dog crate in the living space you use and let the dog get used to to.
   The dog will be curious and investigate.
   
2. Now work on this curiosity by tossing a few treat into the crate, a few centimetres to start.
   You just sit back and watch.
   Praise the dog even when it puts a foot in the crate to get the treat.
   
3. Now toss the treat further into the crate.
   Praise the dog for getting further into the crate.
   Keep going till your dog is all the way in the crate.
   Sit by the crate and praise whilst your dog is still in the crate.
   
4. Keep repeating till the dog is comfortable with going into the crate.
   Give the dog a meal in the crate.
   Just place the bowl at the far end of the crate, leave it and watch.
   Repeat this till the dog eats all meals in the crate.
   
5. Now walk away from the crate when the dog goes in to eat the meal.
   Not too far to start with.
   
6. Use a toy stuffed with treats, such as a Kong, leave it in the crate and let the dog discover it.
   Keep repeating till the dog settles down in the crate to get the food out of the toy.
   
7. Again walk away from the crate.
   Try to let the dog stay in the crate getting the treat out of the Kong.
   
8. Start pushing the door to close it, a little at a time.
   Continue till it is almost closed.
   This will allow the dog just to come out when it wishes.
   You can just sit in view of the dog, just to reassure the dog without speaking.
   
9. When the dog is very happy in the crate start closing the door but do not locked it.
   Gradually extend the period.
   Always stay close, we do not want the dog to get alarmed.
   
10. If all going well, you can go out of sight and come back every few seconds, building the time up.
    Your returning, not too close to the crate, is to observe and not speak to your dog, if he is happy just leave him again.
    

Using this slow and gradual method, your dog is happy in his crate and it is reassuring you, that he is perfectly safe and content.
This slow process with help prevent crate training separation anxiety in your dog.
Remember praise and reward when he does what you want, in this work when he is in the crate.